Evolution of spiral galaxies .7. Time evolution of the radial distributions of abundances

In this work, the time evolution of the radial distributions of elemental abundances in the disks of galaxies is analyzed; in particular, we investigate whether they become flatter, steeper, or remain equal with time. In order to do this, observational data related to elemental abundances and metallicity estimates are briefly reviewed. Most of them refer to our Galaxy, but when possible, other spiral galaxies' data have been included. We show how the traditional view of steeper abundance gradients at later times may be questionable and how recent observational data sets are not in contradiction with the opposite behavior. Theoretical trends are deduced from the application of the multiphase model of chemical evolution, developed by Ferrini and collaborators and successfully used to describe the galactic components and different morphological type galaxies. In particular, we analyze the time evolution of the main properties of the following spiral galaxies: NGC 224, NGC 300, NGC 598, NGC 628, NGC 3198, NGC 6946, and the Milky Way. We show that the radial distributions of elemental abundances may flatten with time if we assume isolated galaxy evolution. The rate for local metallicity enrichment varies with the galactocentric radius and the morphological type, being higher for the central regions and more intense for the early types. The flattening rate of abundance distributions is larger for these types of galaxies, while in the latest types the radial gradient remains almost constant with time.